Remember them being a big deal in early arcs?
Spoilers ahead!
Summary:
- Hand signs were a major element of many fights in early Naruto, but they almost disappeared by the end of the series.
- Many techniques in the later parts just didn't require them in the first place.
- However, it is also one of the elements that simply had no place in the late arcs of the series.
If you remember the early arcs of Naruto, then you might remember how much focus there was on hand signs, or hand seals.
Especially in the Land of Waves arc this was a very big deal: Haku being able to make them with just one hand was considered an incredibly impressive feat. Moreover, some techniques required a huge amount of them, with the most notable being Water Dragon Bullet, performed by Zabuza and Kakashi, which used 44 seals.
That said, the further you watch the series, the less you see hand signs being used. Fans wonder if this actually means something: were they not required, after all, or is there another reason for this?
A logical explanation
The answer is actually pretty complicated. The logical explanation seems simple at first, though: better shinobi simply don't need to use as many seals for their jutsu. That, however, doesn't explain Kakashi and Zabuza using the full sequence of seals for the aforementioned Water Dragon Bullet, as both were noted to be highly skilled.
Another reason is that a lot of techniques in the latter parts of the series required no seals at all. Rasengan is actually notable for that, and that's stated very early in the series — and its variations also don't use any.
Doujutsu — special eyes like Sharingan and Rinnegan — also don't require any hand signs. In general, wielders of most unconventional techniques don't use them: just remember Kakuzu or Hidan.
We do see some hand signs performed occasionally for techniques later in the series, but it's mostly just one or two. The most notable example late in the series is actually Madara, who has to use Susanoo to make multiple hand signs at once — which is apparently required for summoning meteors.
It's one of the elements of the world that was slowly phased out
However, the general trend indicates that there's more to that than just powercreep and switching to more unusual techniques. Many elements of early Naruto are never brought up later in the series.
Hardly anyone ever uses the substitution jutsu the more the anime goes on: replacing yourself with a nearest log is useful in fights, but the mechanics are never explained, and that makes battles anticlimactic. No wonder Kishimoto actively tried to avoid utilizing that.
Perhaps something similar explains the lack of hand signs. Using long chains of them for strong and complex techniques would make fights look bad, but in the opposite way: it just breaks the flow of the fight, as shinobi would have to spend a lot of time on them.